1. Field of the Invention
The invention relates generally to a impact printer and, more particularly, to a printer in which a printing fluid is ejected from a nozzle.
2. Description of the Prior Art
Printers of various kinds have been which employ droplets for printing by depositing discrete drops of printing fluid such as ink on a recording such as a paper sheet in a predetermined pattern. Some of these printers have used static pressure to ex the ink through an orifice to produce a stream of droplet and others of these printers, known as ink jet drop-on-demand printers, have been developed which eject a small of ink only upon electrical command.
While printers of the type described experienced significant improvement and development the years, such printers suffer from a number of serious limitations particularly with respect to the tradeoff must be made in formulating suitable printing inks. For example, for short drying time a rapidly drying ink would be desirable, but such an ink dries in the nozzle during dormancy time of the printhead which creates a maintenance problem. Should one try to solve the problem by a print sheet penetrant in the ink, then drying maintenance are acceptable, but the ink may spread in print sheet which lowers print quality.
To maintain high print quality and printhead maintenance, the present state of the art high water content inks containing highly water dyes with low levels of ionic salt impurities which are likely to precipitate from the ink on evaporation of water at the nozzle surface. These dyes generally suffer the disadvantage of poor waterfastness and poor archivality.
Additional concerns regarding ink jet printing are printhead lifetime and reliability. Often printhead lifetime is limited by corrosion resulting from ink components required for a good ink formulation. It has been shown in the art that the dye and the ions present in inks are the major culprit causing printhead failures. If the pH is too high or too low these can readily corrode the electrical contacts through or pinholes in the protective layers. Other common for example, chloride ions, even at low levels can cause corrosive failure over long periods of time.
While many of the cited problems have solved for low usage, low throughput serial printers, 50 to several hundred nozzles per printhead, the printhead lifetime reliability problem becomes formidable when contemplating page-wide printing with ink printing technology. In this case one would of as many as 2,400 nozzles or more. Furthermore, to print a color image would require three color arrays and in some cases one black nozzle array. It is clear therefore, that the reliability problem for color page printing is formidable by simple extensions of existing technology.
It is therefore the object of this invention to disclose an ink jet process that replaces the ink with a colorless marking fluid which will create a latent image developable in a subsequent step. If the dye is omitted and a simple fluid used then the maintenance of the printhead and its lifetime can be significantly enhanced.
Other prior art imaging processes are known in which a latent image is produced by some colorless marking fluid, and the latent image is developed in a subsequent operation. For example, U.S. Pat. No. 3,265,522 discloses a copying process in which an original to be copied is heated while in contact with an oil so that the oil evaporates from the surface of the original and condenses on a copy surface to form a latent image which is then developed with a colored powder.
U.S. Pat. No. 3,444,809, et al, discloses a reproduction process in which an oil latent image is formed on a support. The oil latent image is developed with a thermoadhesive powder. The thermoadhesive powder image is then heated and transferred to an image receiving sheet where it is developed by a developing powder.
U.S. Pat. No. 4,683,191 discloses an imaging system in which a latent liquid image is formed on a substrate and contacted with toner powder which can exist as a supercooled liquid. The toner powder is then allowed to solidify.
U.S. Pat. No. 3,963,338 relates to an image projector in which an image sheet has a layer of a dry etchant powder which can be modified by a manually applied writing fluid containing an etchant activator to produce a desired image for projection.
All of the cited references refer to the reproduction of existing images, but none of the cited references suggest the creation of a latent image on a print sheet by an ink jet printhead projecting a dyeless marking fluid and subsequently developing and fixing the image to the print sheet to provide a visual image of the desired pattern defined by the control signals by which the ink jet printhead is selectively actuated.